RESEARCH ARTICLE
Early evolution of nocturnal behavior in cockroaches documented by a new Coniacian (Late Cretaceous) amber fossil from Japan
2026 Volume 30 Pages 99-108
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2026 Volume 30 Pages 99-108
Well-preserved insect fossils in amber provide detailed morphological information. Mesozoic cockroach fossils are typically preserved as impressions, but many specimens have recently been discovered from the mid-Cretaceous Cenomanian Kachin amber (ca. 99–98 Ma). However, cockroach fossils from later in the Cretaceous are rare. Here, we report a new Coniacian (Late Cretaceous, ca. 87–86 Ma) cockroach, Ovaliblatta iwakiensis gen. et sp. nov., based on a fossil in amber from the Kohisagawa Member of the Tamayama Formation (Futaba Group) in Iwaki, Fukushima, Japan. Ovaliblatta iwakiensis gen. et sp. nov. is tentatively assigned as a member of Ectobiidae. The antennae, cerci, and tergum of Ovaliblatta iwakiensis gen. et sp. nov. have numerous trichoid sensilla, similar to those of extant nocturnal Ectobiidae. This suggests that Ovaliblatta iwakiensis gen. et sp. nov. represents an early example of the evolution of nocturnal behavior in cockroaches. This is the first record of a cockroach fossil preserved in amber from the late Coniacian and the first such record from Japan.
ZooBank registration: urn:lsid:zoobank.org:pub:AF30CED2-6F01-48EE-9D44-A61EE910378A
Blattaria sensu stricto (i.e., cockroaches) play an important role in terrestrial ecosystems as decomposers. Extant cockroaches are highly diverse, with ca. 6,700 scientific names across all ranks, both valid and invalid, and ca. 4,600 valid species distributed worldwide (Beccaloni, 2014). Cockroaches are also abundant among insect fossils, with over 110,000 sedimentary specimens and 5,000 amber specimens collected to date (Wappler and Vršanský, 2022). The oldest fossil record of a cockroach is from the earliest Late Carboniferous (Namurian) Tupo Formation in China (Zhang et al., 2013).
Many cockroach fossils have been reported from the Cenomanian (Late Cretaceous, ca. 99–98 Ma) Kachin amber deposits in northern Myanmar, representing 11 families, 28 genera, and 36 species as of 2021 (Ross, 2021). In recent years, the number of cockroach species reported from the Kachin amber has increased significantly, with a total of 97 species and over 4,000 specimens now known (Vršanský, 2025; Vršanský and Kobová, 2025). These include many extinct families (e.g. Blattulidae Vishniakova, 1982; Manipulatoridae Vršanský and Bechly, 2015; Umenocoleidae Chen and T’an, 1973) and several extant families (e.g. Blaberidae Saussure, 1864; Corydiidae Saussure, 1864), highlighting the remarkable diversification of cockroaches during the mid-Cretaceous. Mesozoic cockroach fossils have also been found in amber deposits in Lebanon, France, Taymyr (Russia), Hungary, and New Jersey (U.S.A.) (Vršanský, 2004, 2008, 2009, 2019; Sendi and Azar, 2017; Sendi et al., 2023; Szabó et al., 2023, 2024). However, cockroach fossils preserved in amber from the Late Cretaceous are rare. To date, these have only been reported from the Turonian (ca. 94–89 Ma) New Jersey amber (Vršanský, 2004) and the Santonian (ca. 86–83 Ma) Ajkaite amber (Szabó et al., 2024).
The Japanese fossil record of cockroaches is limited to impressions from the Upper Triassic Mine Group (Ominé) in Yamaguchi (Fujiyama, 1973), the Lower–Middle Jurassic Toyora Group in Yamaguchi (Fujiyama, 1974), and the Lower Cretaceous Tetori Group in Fukui (Oyama et al., 2021). Additional fragmentary reports have not been formally described.
Here, we describe a Late Cretaceous (Coniacian, ca. 87–86 Ma) cockroach fossil preserved in amber from the Futaba Group of Fukushima, Japan. This represents the first record of a cockroach fossil preserved in amber from the late Coniacian and the first such record from Japan.
The Futaba Group is distributed along the Pacific coast of Fukushima in northeastern Japan and is subdivided into the Ashizawa, Kasamatsu, and Tamayama formations (Ando et al., 1995; Kubo et al., 2002). The Tamayama Formation is subdivided into the Kohisagawa and Irimazawa members (Ando et al., 1995; Kubo et al., 2002). The Kohisagawa Member yields the insect-bearing amber (hereafter “Iwaki amber”), which dates to the Coniacian (Late Cretaceous, ca. 87–86 Ma). In addition to the cockroach fossil described herein, a new species of microscopic parasitic wasp (Archaeromma chisatoi Aiba and Inose, 2024) and a new genus and species of true bug from the family Microphysidae Dohrn, 1859 (Iwakia longilabiata Aiba, Soma, and Inose, 2025) were recently reported from Iwaki amber. For additional details on the locality and geologic setting, see Aiba et al. (2023, 2025).
The amber fossil containing the cockroach specimen described here was discovered by Chisato Suzuki and is reposited in the collections of the Fukushima Museum in Fukushima, Japan, under catalog number FM-N202200014. The amber was thinly sliced, and its surfaces were polished using an abrasive. Observations were performed using a Leica M205C stereomicroscope (Leica Corporation, Wetzlar, Germany). Thin, translucent portions of the amber were observed at low magnification using an Olympus CX43 optical microscope (Olympus Corporation, Tokyo, Japan). The amber specimen was immersed in camellia oil for photography. Photographs were taken and measurements were obtained using a Leica MC170 HD microscope camera (Leica Application Suite Version 4.1.3, Leica Corporation, Wetzlar, Germany) and an Olympus TG4 optical microscope (Olympus Corporation).
Order Blattodea Brunner von Wattenwyl, 1882
Superfamily Blaberoidea Saussure, 1864
Family Ectobiidae Brunner von Wattenwyl, 1865
Ovaliblatta gen. nov.
ZooBank lsid: zoobank.org:act:E478E8B6-1BDF-4951-98FB-B7DF32328E0E
Type species.—Ovaliblatta iwakiensis gen. et sp. nov.
Etymology.—From ovalis (Latin for ‘oval’) and blatta (Latin for ‘cockroach’).
Diagnosis.—As for the type species by monotypy.
Ovaliblatta iwakiensis gen. et sp. nov.
ZooBank lsid: zoobank.org:act:A1CF9312-A254-4C62-8011-BF79C1EDD804
Diagnosis.—Nymph, sex unknown: Body small, 8.42 mm long (from apex of head to abdomen tip), 5.60 mm wide, ovate, dorsally swollen, pale brown, completely lacking tegmina and wings. Head relatively small (ca. 2.4 times narrower than the pronotum). Proximal segments of flagellum beyond second flagellomere extremely dense and short. Legs long and robust. Pronotum with two rows of longitudinal dark stripes, metanotum with four, and abdomen with five rows of longitudinal dark stripes. Cerci parallel and extremely long (1.5 times longer than pronotum), not fusiform (basally thick and apically narrow, tapering).
Holotype.—FM-N202200014, individual in an amber almost completely preserved on its dorsal (Figure 1A) and ventral sides (Figure 1B).
Type locality and horizon.—The specimen was collected from the muddy sandstone layer of the Coniacian (Upper Cretaceous, ca. 87–86 Ma) Kohisagawa Member (Tamayama Formation, Futaba Group), exposed at an outcrop located in a tributary of the Kobisa River in Iwaki, Fukushima, Japan.
Etymology.—Named after the city of Iwaki, where the holotype was discovered.
Description.—Nymph, Sex unknown: Body small, oval, dorsally swollen, pale brown, completely lacking tegmina and wings.
Head (Figure 1C): Hypognathous, relatively small, forming an almost equilateral triangle, 1.13 mm long, 1.62 mm wide. Eyes faintly preserved, not protruding from head outline. Ocelli not clearly visible. Left and right antennae (Figures 1C, D; 4B) preserved only at the base, 2.30 mm and 2.20 mm remaining portions of the left and right antennae, respectively; scape cylindrical, faintly visible; pedicel cylindrical, 0.24 mm long, 0.12 mm wide; first flagellomere cylindrical and about the same length as pedicel but slightly swollen, 0.24 mm long, 0.16 mm wide, with sensilla chaetica (Figure 1C); proximal segments of flagellum from the second to the 20th flagellomere very short and dense (10–30 μm long); from the 21st to the 37th flagellomere slightly longer (30–40 μm long); preserved distal six flagellomeres with clearly visible borders (ca. 50 μm long). Two types of sensilla chaetica arise on each flagellum (Figure 1D): one short type, hair-like and sharply tapered, densely anteriorly directed (ca. 50 μm long); the other long type, hair-like and very thin, sparsely arising vertically from the flagellum (ca. 150 μm long). Trichoid and grooved basiconic sensilla absent or, if present, not visible. Maxillary palpi (Figure 1E) relatively long, with third to fifth segments preserved, each of equal length (ca. 0.6 mm long) and covered with dense trichoid sensilla.
Pronotum (Figures 1A, 4A) short and transverse, 2.10 mm long, 3.89 mm wide, with two dark-colored longitudinal stripes and short setae. Mesonotum extremely transverse and half the length of pronotum, 1.10 mm long, 5.10 mm wide, with four dark-colored longitudinal stripes and short setae. Metanotum the same length as mesonotum, 1.10 mm long, 5.40 mm wide, with four dark-colored longitudinal stripes and short setae.
Legs (Figures 2, 4C–E) long and robust. Each femur without chaetae, but tibiae and tarsi with numerous setae and speckled dark coloration. Pulvillus not visible on each tarsus, being either underdeveloped or absent. Fore legs cursorial (Figures 2A, 4C): femur robust, ca. 3.0 mm long and 0.50 mm wide, with a small terminal spine but details not visible; tibia short and robust, 1.50 mm long and 0.40 mm wide, with at least eight spurs; tarsi five-segmented (tarsomeres 1 to 5 measuring 0.75, 0.41, 0.30, 0.28 and 0.55 mm, respectively). Mid leg cursorial and asymmetrical (Figures 2B, C, E; 4D): femur robust, ca. 3.0 mm long and 0.50 mm wide; tibia long and robust, about 2.3 times as long as fore tibia, 1.50 mm long and 0.40 mm wide, with at least 13 spurs; right tarsus (Figure 2B) five-segmented (tarsomeres 1 to 5 measuring 0.99, 0.36, 0.27, 0.17, and 0.37 mm, respectively), but left tarsus (Figures 2C, 4D) four-segmented (tarsomeres 1 to 4 measuring 1.25, 0.52, 0.18 and 0.48 mm, respectively). Hind leg cursorial (Figures 2C, D; 4E): femur robust, 3.50 mm long and 1.12 mm wide, with one terminal spine and at least four evenly spaced fine spurs at the anteroventral margin; tibia long and robust, about 1.4 times as long as mid tibia, 5.10 mm long and 0.50 mm wide, with 28 spurs; tarsi (Figures 2C, 3E) five-segmented (tarsomeres 1 to 5 measuring 1.56, 0.58, 0.41, 0.20 and 0.48 mm, respectively). Tarsal claw thin (ca. 0.25 mm long). Arolia large, as long as tarsal claw.
Abdomen (Figures 1A, B; 3; 4A) broadly rounded; terga I–IX visible (terga I to IX measuring 0.35, 0.48, 0.45, 0.48, 0.45, 0.48, 0.48, 0.27 and 0.17 mm, respectively) with five dark-colored longitudinal stripes. Each tergum with short setae and 10 to 12 small chaetica patches, from which 20 to 30 sensilla chaetica arise (Figures 3A, B; 4G). Supra-anal plate semitransparent and protruding, with hind margin slightly concave medially, 0.68 mm long, 2.09 mm wide (Figure 3C). Subgenital plate visible from dorsal side because the supra-anal plate is semitransparent (Figures 3C, D; 4F); asymmetrical, triangular, constricted at the middle, both sides bent dorsally. Two small styli (Figures 3D, 4F) visible; asymmetrical, far apart; interstylar distance ca. 0.45 mm; right stylus 0.25 mm long and 0.10 mm wide, larger than the left; left one small and thin, 0.20 mm long and 0.05 mm wide. Cerci completely preserved (Figures 3C, E; 4F), parallel and very long, about 1.5 times as long as pronotum, 3.08 mm long and 0.42 mm wide at base, flattened, basally thicker and apically narrower, tapered; apical half dark-colored with 13 segments (cercal segments I to XIII measuring 0.23, 0.11, 0.11, 0.10, 0.23, 0.16, 0.22, 0.23, 0.30, 0.38, 0.28, 0.33 and 0.52 mm, respectively). Each segment with numerous short sensilla chaetica, ca. 60 μm long, and sparse long sensilla chaetica, ca. 160 μm long; basal segments I to VIII with campaniform sensilla? visible (Figures 3C, E; 4F).
Comparison.—Based on the following characteristics, FM-N202200014 most closely resembles the family Ectobiidae: a relatively small and pale brown body, pronotum with two dark-colored longitudinal stripes, well-developed legs and anteroventral margin of femur with a row of spines, a protruding supra-anal plate, and two small short and asymmetrical styli (Asahi et al., 2016; Komatsu and Ito, 2023; Rentz, 2014; Yanagisawa, 2022). However, although details are not clearly visible, the forefemur has small apical spines; the protruding supra-anal plate lacks further specialization; the asymmetry of the stylus may also be due to taphonomic bias. Therefore, we tentatively refer FM-N202200014 to the family Ectobiidae. The morphology of the widened basal antennae is rather unique and occurs only in a few extant species among the family Ectobiidae (Vršanský, pers. comm.). This suggests that FM-N202200014 belongs to a new genus.
The Ectobiidae, formerly known as Blattellidae, is the largest family in Blattodea, comprising five subfamilies, approximately 220 genera, and 2,400 species (Beccaloni and Eggleton, 2013). Fossil records of the family Ectobiidae from the Mesozoic are scarce, with only 11 species in five genera known (Mitchell, 2022). The oldest fossil includes four species of the genus Piniblattella Vršanský, 1997 from the Lower Cretaceous (Aptian) of Siberia (Vršanský, 1997) and two species of the genus Piniblattella from the Lower Cretaceous (Aptian) of Brazil (Lee, 2016). Two Piniblattella species have been reported from the Lower Cretaceous (Barremian) of China (Vršanský, 2005; Gao et al., 2019). One species of the genus Nehevblattella Vršanský, 2004 has been reported from the Upper Cretaceous (Turonian) of Israel (Vršanský, 2004). All of those fossils are preserved as impressions. The reports from amber are one species each of the genera Ectooviinae Sendi, 2021, Caligoptera Sendi, 2021 and Latiblattella Hebard, 1917 from the Middle Cretaceous of Myanmar (Sendi, 2021). Most recently, Neoblattella nechapetomu Vršanský, Sendi and Azar, 2023 was reported from amber from Lebanon.
Ectobiidae fossils from the Cenozoic are abundant (Vršanský, 1997, 1999, 2002; Anisyutkin et al., 2008; Wei and Ren, 2013). In the Cenozoic record, Ectobiidae fossils are classified into five subfamilies, 15 genera, and 13 species, with many undescribed species (Greenwalt and Vidlicka, 2015). Latiblattella basaltica Vršanský, Poschmann and Vidlicka, 2022 was recently reported from the Enspel.
Comparing FM-N202200014 with five Mesozoic genera and 15 Cenozoic genera, the following characteristics clearly differentiate FM-N202200014 from any known genus: a dorsally swollen, oval body (other fossils are flattened or broadly oval); extremely dense and short proximal flagella (other fossils are not as dense); longer than the pronotum and not fusiform cerci (other fossils are shorter than the pronotum and fusiform or elongated fusiform). These characteristics not only distinguish FM-N202200014 from other fossils of the family Ectobiidae but also from any other cockroach fossils reported from Cretaceous amber.
Based on these comparisons, FM-N202200014 can clearly be distinguished from any previously reported fossil cockroach and all extant genera of the Ectobiidae and represents a new genus. This new genus, Ovaliblatta gen. nov., may belong to a new subfamily. However, due to insufficient morphological information, the subfamily is left undetermined here.
Ontogenetic stage.—The cerci of FM-N202200014 are highly developed, elongated, and flattened, with distinct internodes, clearly exhibiting 13 segments and being densely covered with numerous setae (Figure 3C–E). In extant species, the cerci of nymphs are typically underdeveloped, small, not flattened, with indistinct segments and few setae (Sen, 2013). However, these features alone are insufficient to identify FM-N202200014 as an adult. This is because several fossil cockroach nymphs with highly developed cerci have been reported from the Cretaceous (Vršanský, 2009; Vršanský et al., 2013; Vršanský et al., 2019). In FM-N202200014, the subgenital plate is underdeveloped relative to what would be expected of an adult male. We therefore interpret FM-N202200014 as a nymph. Styli are present in nymphs of both sexes, so the sex of FM-N202200014 cannot be determined.
Remarks.—The left tarsomere consists of four segments on the middle leg (Figure 2C). This represents regeneration rather than malformation. Compared to Figure 2B, the middle tarsomere t2 in Figure 2C is markedly elongated while the other tarsomere segments are normal. This t2 is considered to be the regeneration of t2+t3 (see Li and Huang, 2022).
The robust legs of Ovaliblatta iwakiensis gen. et sp. nov. indicate fossorial habits, while the large arolium may suggest tree climbing. The vertical stripes in its body coloration are thought to represent warning coloration. The genus Balatronis Šmídová and Lei, 2017 is known from a Cretaceous nymph fossil with warning coloration (Šmídová and Lei, 2017), and its body coloration resembles that of FM-N202200014. However, as mentioned above, it can be clearly distinguished based on body shape and antenna morphology.
Extant cockroach antennae are mostly short (3–20 μm) trichoid sensilla with rounded tips (Sen, 2013). However, those observed in Ovaliblatta iwakiensis gen. et sp. nov. are chaetic rather than trichoid, being more than 50 μm long and tapered at the tip (Figure 1C). Ovaliblatta iwakiensis gen. et sp. nov. is characterized by a high density of sensilla chaetica on its antennae and cerci (Figure 1D), which sense mechanical stimulation (Toh, 1977; Staudacher et al., 2005; Watanabe et al., 2012). The proximal segments of the flagellum after the second flagellomere are very dense and short, increasing the density of the sensilla chaetica. Additionally, small patches of sensilla chaetica are scattered across each tergum (Figure 3B). Therefore, it is plausible that Ovaliblatta iwakiensis gen. et sp. nov. was highly sensitive to mechanical stimuli and capable of detecting subtle environmental movements.
Many cockroach fossils from the mid-Cretaceous Kachin amber have large, well-developed compound eyes (e.g. Huablattula Qiu, Wang and Che, 2019; Manipulatoides Li and Huang, 2023). Taniguchi et al. (2021) examined the morphology of the compound eyes and sensory organs of the antennae of Huablattula hui Qiu, Wang and Che, 2019 in detail. Their findings indicate that H. hui exhibits well-developed compound eyes and relatively few sensory organs, consistent with diurnal behavior in bright habitats.
Many extant cockroaches are nocturnal and live in forests and caves (Bell et al., 2007). The morphology of Ovaliblatta iwakiensis gen. et sp. nov., characterized by large undeveloped compound eyes and numerous sensilla chaetica on the antennae, cerci, and tergum, suggests that this species was nocturnal (Figure 5), similar to extant cockroaches. Although behavioral inferences should be made with caution, these features suggest that nocturnal behavior may have evolved within the Ectobiidae by the Late Cretaceous.
Ovaliblatta iwakiensis gen. et sp. nov. represents the only known Late Cretaceous occurrence of Ectobiidae preserved in amber. The fossil record of the Ectobiidae remains limited, and this new specimen therefore constitutes an important source of data for future research on the evolutionary history of the family.
We thank Chisato Suzuki for discovering the specimen and Hiroaki Inose (Fukushima Museum) for giving us the opportunity to study it. We thank Peter Vršanský (Slovak Academy of Sciences), one anonymous reviewer, and the editor-in-chief for their constructive comments. This work was supported by JSPS KAKENHI Grant Number JP24K17161.
H. A. initiated the study, drafted the manuscript, and compiled all the figures. O. N. revised the manuscript and provided taxonomic input. Both authors contributed to the writing of the manuscript.
